Pipe empty process

Hello Carlos,

When you say "pipe empty", are you referring to column separation occurring at an air valve, due to a pressure drop from a surge event? If so, HAMMER does have the ability to model this situation, though with a few limitations:

1) The air pocket is assumed to take up the entire cross section of the pipe.
2) The air pocket is localized at the point of formation (the air valve node). So, the extent of the air pocket along the pipeline is unknown and the air-liquid interface is assumed to be at the node location. (by default, unless using the Extended CAV calculation option)
3) Air pockets entering an air valve can only exit the system through the same point. Basically it is assumed that the pocket cannot be swept downstream and expelled elsewhere.  

The air pocket formation occurs automatically, when the hydraulic grade at the air valve drops to the air valve elevation.

To check if the air valve was adequate to prevent subatmospheric pressure in the system, you would look at and/or animate a profile path of the system, using the Transient Results Viewer. The blue line in the transient envelope will show you the lowest that the pressure reached and the green line will show the ground elevation. Remember that air valves typically only provide protection in the immediate vicinity of the valve, so it may not necessarily be possible for an air valve alone to provide enough protection. Close examination of the profile path after the simulation should make this more clear. You can read more about air valve modeling here:

Modeling Reference - Air Valves

As for the maximum velocity of water column - no, there is no way to have the program design the air valve size based on this. You would need to check the results, adjust as necessary, re-run the simulation, check the results, and so forth.

I hope this helps.

Jesse:

Thanks for your post.

Really,  my question is if Hammer is able to simulate the complete drainaje of the pipe in oder to check the air valves arrangement (if is able to maintain atmosferic pressure during all the time and along the whole pipe)

Carlos

The basic assumption in HAMMER is that pipes are flowing full. HAMMER has a limited ability to model air in the system, but the larger the volume of air introduced, the less accurate the results will be. (see limitations mentioned in my last post) So, I would not recommend trying to model a system becoming completely empty. Maybe you could explain a bit more about what you're trying to accomplish? Depending on exactly what transient event you're trying to simulate, we may be able to help you find a better way to model what you need.

Related threads that may help:

http://communities.bentley.com/products/hydraulics___hydrology/f/5925/p/63816/159413.aspx#159413

http://communities.bentley.com/products/hydraulics___hydrology/f/5925/p/57871/137262.aspx#137262